North Korea leader Kim Jong Un has inspected a newly built submarine and ordered officials to further bolster the country's military capability, state media reported Tuesday, as the North is increasing its pressure on the United States ahead of the possible resumption of nuclear diplomacy.

Last week, North Korea said it may lift its 20-month suspension of nuclear and missile tests to protest expected military drills between the United States and South Korea that North Korea views as an invasion rehearsal.

The Korean Central News Agency reported Kim expressed "great satisfaction" with the submarine after learning about its operational and tactical data and weapon systems.

Kim "stressed the need to steadily and reliably increase the national defense capability by directing big efforts to the development of the naval weapons and equipment such as submarine," according to KCNA.

KCNA didn't say exactly when and where Kim's inspection of the submarine occurred. It said the submarine's operational deployment "is near at hand."

The construction of a new submarine suggests North Korea has been increasing its military capability despite nuclear diplomacy with the U.S. That began early last year. North Korea has repeatedly said it's willing to abandon its nuclear program in return for political and economic benefits.

It wasn't immediately known exactly what kind of a submarine North Korea has built. But its efforts to develop submarine-launched missile systems are a serious concern for rivals and neighbors because missiles from submerged vessels are harder to detect in advance.

Before it entered talks with the United States, North Korea claimed to have successfully test-fired ballistic missiles from submarines, though many outside analysts say North Korea likely remains years away from having an operational system.

According to a South Korean defense report in 2018, North Korea has 70 submarines and submersibles.

The North's disclosure of a new submarine came after Kim and President Donald Trump held their third summit at the Korean border late last month and agreed to resume nuclear negotiations. The countries' nuclear diplomacy remained stalled since the second Kim-Trump summit in Vietnam in February fell apart due to squabbling over U.S.-led sanctions on North Korea.